Hi,
First off, it would be interesting to know if anyone else with a Core i7 is seeing it reported as just having the one core.
Ok, to hyperthreading. We try to detect hyperthreading and if so we set the number of cores to number of actual physical cores. So if you have a single core P4 with hyperthreading we report it as just one core and ignore the hyperthreaded core. This is also why we only detect 4 cores on a Core i7 instead of 8. This is because we found that hyperthreading was slowing renders down in some cases and, as dwilson has found, on older processors hyperthreading only gets you a small speed increase anyway. 14% would be about typical.
With Core i7/Nehalem hyperthreading is apparently much better, and I think in this case we might need to add a check to see if a CPU is Core i7/Nehalem and if so count the hyperthreaded cores. That would mean you'd see 8 cores on a Core i7. There is a different issue here though, in that TG2 has scaling problems with rendering above 4 cores, it starts to get slower instead of faster the more cores you add. On Windows I think it might go ok up to 6 cores IIRC. There is no doubt that the Core i7 is a great CPU for TG2 though.
CPU detection on Windows, especially across the range of OSes we support, is a really nuisance.
Regards,
Jo